Triboelectrostatic Separation Process Research Articles

Experimental and numerical analysis of a tribo-electrostatic separation process of micronized plastic particles using rotating disk electrodes

ABSTRACT This paper reports an experimental and numerical analysis of a tribo-electrostatic separation process based on a fluidised bed tribo-charging system and two rotating disks connected to two high-voltage DC supplies of opposite polarities. The experiments were performed using a granular mixture composed of µm-size white Polyvinylchloride particles (WPVC) and grey Polyvinylchloride particles that contain a small percentage of carbon (GPVC). A numerical analysis supported the experimental results. It was deduced that the separation outcome is efficient and depends on the high-voltage level, the rotating speed of the electrodes and the fluidisation rate.

MODELLING AND OPTIMIZATION OF THE WASTE MICRONIZED PLASTICS RECOVERY BY TRIBOELECTROSTATIC SEPARATOR

Triboelectrostatic separation of millimeter-size particles is widely used in the recycling industry of plastics. However, the separation of micronized particles needs still improvement due to the aerodynamic forces of such small particles. This paper is aimed to carry out an experimental investigation of a triboelectrostatic separation process based on a pair of rotating disks supplied by two high-voltage DC supplies of opposite polarities. The granular samples used in this paper are composed of micronized white pure virgin PolyVinyl Chloride particles (WPVC) and gray PolyVinyl Chloride particles (GPVC) of average size 50 m. Moreover, the methodology of experimental designs was used for the experimental modelling and optimization of the separation process. It was deduced that the separation recovery is efficient and depends on several factors: the high-voltage level, the rotating speed of the disks, the fluidization rate and inter-electrodes spacing. The results obtained showed that the applied voltage remains the most significant factor in the separation process. The best separation performance was obtained for an applied voltage of 20 kV and a disk rotation speed of 100 rpm.

Experimental and numerical analysis of a new tribo-electrostatic separator with coaxial cylindrical electrodes for plastic binary granular mixtures

This paper is aimed to the description of a new tribo-electrostatic separation process where the top part of the separator is constituted by two coaxial electrodes and the bottom part comprises two cone-shaped electrodes. An experimental and a numerical analysis were carried out in which the main significant factors were investigated. The experiments carried out on three different binary mixtures of mm-size PA (polyamide), PC (polycarbonate) and PVC (polyvinyl chloride) particles showed that more than 80% of the total mass is recovered with high purity values up to 90%.

Effect of hammer and pin milling on triboelectrostatic separation of legume flour

The effect of hammer milling on the efficiency of a triboelectrostatic separation process to produce protein-, starch-, and seed-coat fibrous- enriched fractions from navy bean flour was investigated and the results were compared with previously published data for pin milled flour. Results revealed that samples collected from the middle and top part of the plate had significantly higher protein content and therefore lower starch content than the samples collected from the bottom of the plate. The bin that was located on the bottom of the separator, directly below the entrance of the ejector nozzle, contained higher amounts of seed-coat fibrous particles. A maximum protein content of 39.3 ± 0.7% and 32.6 ± 0.1% occurred on the middle/top and bottom part of the plate for optimum operating conditions. Hammer milling yielded a larger average particle size and a lower triboelectric separation efficiency compared to pin milling.

Triboelectric Charging of Granular Polymers Previously Exposed to Dielectric Barrier Discharges in Atmospheric Air

The aim of the present article is to study the feasibility of continuous dielectric barrier discharge (DBD) treatment of granular plastic materials in view of improving their triboelectric charging ability, and assessing the effectiveness of associating plasma treatment with the triboelectrostatic separation process. The effects of the following DBD parameters were studied: the amplitude and the frequency of the applied high voltage, the thickness of the dielectric barrier, the distance between the electrodes of the reactor as well as the speed of the conveyor that was used for the transfer of the granular materials though the nonthermal plasma zone. The study was carried out on millimeter-sized polyethylene particles. It was found that the charge of DBD-treated particles increases with the applied high voltage and decreases with the speed of the conveyor. Both the distance between the electrodes and the thickness of the dielectric barrier have a remarkable effect on the charge acquired after DBD treatment. Within the experimental domain of this study, the frequency of the high voltage does not significantly affect the efficiency of the tribocharging process. Under optimal operating conditions given by the first series of experiments, two distinct triboelectrical series were established, one for treated particles and the other for untreated particles, using eight types of granular plastics [acrylonitrile butadiene styrene, polyethylene (PE), polypropylene, polyvinyl chloride, crystalline polycarbonate, polystyrene (PS), high impact polystyrene, and crystalline polystyrene], Finally, an electrostatic separation experiment was carried out on a plasma-treated PE–PS mixture using a roll type electrostatic separator. The results were then compared with those obtained for an untreated mixture. It was found that plasma treatment improved by about 40% the purity and recovery of the sorted products.

Micronized plastic waste recycling using two-disc tribo-electrostatic separation process

Triboelectrostatic separation of millimeter-size granular mixtures is nowadays widely used in the recycling industry. However, the separation of micronized particles of an average granulometric size of 100 µm is still inefficient. This paper is aimed to carry out an experimental investigation of a triboelectrostatic separation process based on a fluidized bed tribocharging system produced between a pair of rotating aluminum disks supplied by two high-voltage DC supplies of opposite polarities. The granular mixture used in this work is composed of micronized white pure virgin PolyVinyl Chloride particles (WPVC) and gray PolyVinyl Chloride particles that contain a small percentage of carbon (GPVC) of average size 100 μm. Moreover, a homemade method was developed to estimate the purity of the separated products. It was deduced that the separation outcome, in terms of recovery and purity, is efficient and depends on several factors: the high-voltage level, the rotating speed of the disks, the fluidization rate, the total mass of the fluidized bed and the composition ratio of the granular mixture.

Application of tribo-electrostatic separation in the recycling of plastic wastes

Abstract In the last decades, increasing industrial development has led to huge consumption of plastic materials, due to their versatility and low cost. Therefore, the implementation of efficient and environmentally friendly recycling technologies is of great importance. This study proposes an alternative separation process for recycling mixtures of plastic wastes, using a tribo-electrostatic separation process. The methodology adopted in this work was firstly characterization of the polymeric wastes, followed by preparation of the wastes using different unit operation processes (washing, drying, and comminution), tribo-charging, and electrostatic separation of different combinations of plastics (HDPE/PP, LDPE/PP, and PET/PVC). Various parameters were evaluated in the tribo-charging process and the electrostatic deflection. Separation of a mixture of HDPE and PP achieved PP recovery of 92.8% (purity of 95.7%) and HDPE recovery of 95.9% (purity of 93.1%). Recovery and purity values higher than 90.2% and 95.9% were obtained for PP/LDPE and PET/PVC mixtures, respectively. These results demonstrated that tribo-electrostatic separation is a promising and efficient method for use in the recycling of plastic wastes. The process studied enabled significant recoveries of the components at high levels of purity.

Principal Factors of Contact Charging of Minerals for a Successful Triboelectrostatic Separation Process – a Review

Triboelectrostatic separation is a promising method used to separate non-conductive minerals. However, the knowledge about the underlying triboelectrification mechanisms is still very limited. Thus, predicting the separation results and finding proper separation parameters are challenging tasks. This article presents a comprehensive summary of phenomena and factors which play a decisive role in the charging behavior of non-conductors and, by implication, the efficiency of the separation process, such as water and adsorbents layers on the surface, surface roughness, humidity, type of contact, etc. The authors hope that this article opens a way for a systematic approach through basic experiments dedicated to a better understanding of triboelectrification processes.

Experimental Investigation of a New Triboelectrostatic Separation Process for Mixed Fine Granular Plastics

Triboelectrostatic separation of millimeter-size particles is a well-known process, which is widely used in the recycling industry. However, when processing fine particles with an average diameter of 0.1 mm or less, this technique is still inefficient. The aim of this paper is the experimental investigation of a patent-pending triboelectrostatic separation process based on a fluidized bed tribocharging system where the fine granules to be sorted are exposed to the electric field generated between a pair of rotating metallic disks connected to two high-voltage supplies of opposite polarities. The lower parts of the disk electrodes are immersed in the fluidized bed. The experiments were carried out on a granular mixture composed of fine white and gray PVC particles of average size 20 μm. The particles to be separated are positively and negatively tribocharged using the fluidization air provided by a variable-speed blower, and then they are pinned to the disk electrodes of opposite polarities. The separation outcome, in terms of recovery and purity, is highly efficient and depends on several factors: the high-voltage level, the rotating speed of the disks, the interelectrode gap, the thickness of the fluidized bed, and the fluidization rate.

Experimental and Numerical Modeling of a New Tribo-Electrostatic Separation Process for Granular Plastics Mixtures

The paper aims at optimizing the operation of a free-fall electrostatic separator equipped with a novel tribo-charging device for the processing of granular plastic mixtures. Experiments were performed with a mixture of polycarbonate and polyamide granules (cylinders of 1.5 mm in diameter and 3 mm in length). The samples of granules to be charged were introduced in the gap between the two co-axial cylinders of the tribo-charging device, and were put into turbulent motion for 30 s by two oppositely oriented air jets (pressure: 2 bar). Then, the charged particles were left to fall freely between the vertical plate electrodes of an electrostatic separator. A composite experimental design enabled the modeling and optimization of the tribo-electrostatic separation process as a function of the following control factors: applied high voltage, inter-electrode distance, and the inclination angle of the feeding device. Under optimal conditions, the purity obtained is close to 99%. A numerical model of particle trajectories confirms the conclusions of the experimental study. The simulations point out the effect of each control variable on the outcome of the separation process.

Experimental study of the tribocharging process of plastic granular materials on a vibratory feeder device

Triboelectrostatic separation of granular plastics wastes is a technology that is more and more employed in the recycling industry. The paper is aimed at characterizing the tribocharging of Polyvinyl Chloride (PVC), Polyamide (PA) and High Density Polyethylene (HDPE) granules on a vibratory feeder tray covered by a Polyethylene Terephthalate (PET) sheet, in order to evaluate the possibility of using this device in a continuous tribo-electrostatic separation process. A capacitive probe was used to evaluate the surface charge density on the PET sheet. When the tray of the vibratory feeder was grounded, the charge density at the surface of the PET sheet was found to increase slightly after every tribocharging experiment, while the charge of PA granules saturated at 2.6 nC/g. In the case of an isolated PET sheet, its surface charge density is rapidly increasing and tends to saturate, limiting the charge/mass ratio of PA granules at 1.4 nC/g. Similar results were recorded for other tested materials, proving the efficiency of the tribocharging on the PET tray of the vibratory feeder.

Set‐point identification of a free‐fall triboelectrostatic separation process for plastic particles

Identification of the optimal operating conditions and evaluation of their sensibility to changes in certain critical factors are critical issues for the industrial application of electrostatic separation techniques. The aim of this paper is to validate an experimental procedure for optimising the selective sorting of non‐conductive constituents of granular industrial plastic wastes using a free‐fall triboelectrostatic separator.